In some methods and systems of inspection that are known in the art, a sample is induced to emit radiation from an array of spots. For instance, multiple excitation beams may be directed toward the sample in a predetermined geometrical pattern, and the resulting emission from each of the spots on which a beam is incident may then be collected and measured. Such multi-spot configurations can be useful in increasing inspection throughput since multiple locations are inspected in parallel.
As one example of such a system, U.S. Pat. No. 6,465,783, whose disclosure is incorporated herein by reference, describes apparatus and methods for inspecting semiconductor wafers and other types of specimens using parallel charged particle beams, such as electron beams. An emitter array produces multiple beams that propagate along respective beam axes. The beams pass simultaneously through projection lenses and a deflector so as to cause the beams to be focused simultaneously onto respective loci on the surface of the specimen, thus causing each locus to emit secondary electrons. The secondary electrons are detected by a secondary-electron (SE) array including multiple SE-detector units. Each SE detector unit receives and detects secondary electrons emitted from a respective locus.
As another example, PCT International Publication WO 2003/041109, whose disclosure is incorporated herein by reference, describes a high data-rate electron beam spot-grid array imaging system. Embodiments include an imaging system comprising an electron beam generator for simultaneously irradiating an array of spots spaced apart from each other on a surface of an object to be imaged. A detector collects backscattered and/or secondary electrons emitted as a result of the interaction of the spots with the surface of the object to form an image of the irradiated portions of the object surface. A mechanical system moves the substrate in a direction which is nearly parallel to an axis of the array of spots such that as the substrate is moved across the spot array in the scan direction, the spots trace a path which leaves no gaps in the mechanical cross-scan direction.
Other spot-grid array systems, using charged particle or optical excitation beams, are described in PCT International Publication WO 2005/024881 and in U.S. Patent Application Publication 2006/0261261, whose disclosures are likewise incorporated herein by reference.